The aim of this project is to design mechanism-based chemopreventive strategies and to develop surrogate biomarkers for tobacco-related oral carcinogenesis. The 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster cheek pouch model at the post-initiation stage, which mimics oral carcinogenesis in former smokers, will be used. Our preliminary results showed overexpression of leukotriene A4 hydrolase (LTA4H), cyclooxygenase 2 (Cox2) and epidermal growth factor receptor (EGFR) in oral cancer, in this application, we plan to test the hypothesis that inhibition of aberrant arachidonic acid (AA) metabolism and EGFR/ErbB2 will prevent oral carcinogenesis, with the following specific aims: 1. To determine the effectiveness of specific inhibitors of LTA4H, Cox2, and EGFR/ErbB2, as chemopreventive agents against oral carcinogenesis in short-term and long-term experiments. Vve will topically apply bestatin (LTA4H inhibitor), celecoxib (Cox2 inhibitor), or GW2974 (dual inhibitor of EGFR/ErbB2) to DMBA-treated hamster cheek pouches, to determine their efficacy against the, formation of leukotriene B4 (LTB4), prostaglandin E2 (PGE2) and EGFR/ErbB2 autophosphorylation, the expression of LTA4H, Cox2 and EGFR/ErbB2, proliferation, apoptosis, inflammation, and carcinoma formation. These parameters wilt be correlated to develop potential surrogate biomarkers for chemoprevention. 2. To determine the functional roles of LTB4 and PGE2 in promoting oral carcinogenesis by topically applying 20-tri-fluoro-LTB4 or 16,16-dimethyt-PGE2 to hamsters treated with one dose of DMBA. In short-term and long-term experiments, their effects on cell signaling kinases, AA metabolism, ceil proliferation, apoptosis, inflammation, and the development of dysplasia and carcinoma will be examined. The potential surrogate biomarkers will be further studied. 3. To investigate the chemopreventive effects of combinations of the above inhibitors, and to validate the usefulness of the surrogate biomarkers identified in Aim 1. These studies are expected to contribute significantly to the prevention of oral carcinogenesis in former smokers. Some of the agents and biomarkers studied herein may be used for chemoprevention in individuals with leukoplakia and erythroplakia.